WO2023054830A1

WO2023054830A1 - Method for producing terephthalic acid by using high degree of polymerization of polyethylene terephthalate having intrinsic viscosity of 0.75 dl/g or more

Info

Publication number: WO2023054830A1
Application number: PCT/KR2022/006376
Authority: WO
Inventors: 김영범
Original assignee: 김영범
Priority date: 2021-09-28
Filing date: 2022-05-04
Publication date: 2023-04-06
Also published as: JP2023548263A; US20230107495A1; JP7484010B2; EP4155289A1; KR102381508B1; EP4155289B1

Abstract

The present invention relates to a method for producing terephthalic acid from a high degree of polymerization of polyethylene terephthalate having an intrinsic viscosity of 0.75 dl/g or more, wherein (i) the high degree of polymerization of polyethylene terephthalate having an intrinsic viscosity of 0.75 dl/g or more is introduced into a continuous reactor, and then heated and pressurized to prepare a flowable polyethylene terephthalate, (ii) a mixed slurry prepared by mixing an alkali containing an alkali metal, a weak acid salt of the alkali metal, and ethylene glycol is introduced into the continuous reactor through which the flowable polyethylene terephthalate passes, to thereby prepare an alkali metal terephthalate by a neat reaction of the flowable polyethylene terephthalate and the mixed slurry in the continuous reactor, and (iii) the prepared alkali metal terephthalate is dissolved in water, and then foreign materials are removed by filtration and centrifugation, and an acid is added to the alkali metal terephthalate dissolved in water, followed by reaction, thereby producing terephthalic acid. In the present invention, terephthalic acid can be produced from a high degree of polymerization of polyethylene terephthalate having an intrinsic viscosity of 0.75㎗/g or more, which has been difficult to hydrolyze with even an organic solvent due to a high degree of polymerization, with a high yield and favorable process safety, even without the use of an organic solvent.

Description

Method for producing terephthalic acid using polyethylene terephthalate of high polymerization degree having an intrinsic viscosity of 0.75 dl/g or more

The present invention relates to a method for producing terephthalic acid using polyethylene terephthalate having a high polymerization degree having an intrinsic viscosity of 0.75 dl/g or more, and more specifically, producing polyethylene terephthalate having an intrinsic viscosity of 0.75 dl/g or more without using an organic solvent. It relates to a method for producing terephthalic acid in high yield and good process stability by hydrolysis.

For chemical recycling of polyethylene terephthalate (hereinafter abbreviated as "PET"), depolymerization in which the molecular chain is broken at high temperature and high pressure in the presence of ethylene glycol (hereinafter referred to as "EG") solvent or polarity such as alcohol in the presence of acid or alkali A molecular chain decomposition process such as hydrolysis in a solvent is required.

At this time, when the degree of polymerization of PET is not high with IV=0.6 dl/g or less, the following three methods of [Scheme 1] are typically used.

In the first method, dimethyl sulfoxide (DMSO), dichloromethane ( A certain amount of organic solvent such as dichloromethane is mixed to promote the swelling of PET, so that the reaction can be performed under weaker conditions.

[Scheme 1]

[Correction under Rule 91 18.05.2022]

In the second method, as shown in (b) of [Scheme 1], hydrolysis is performed in a polar organic solvent with an alkali such as NaOH, and relatively easily di-sodium terephthalate (TPA-Na ₂ ) and It is decomposed into ethylene glycol (EG), and di-sodium terephthalate is easily converted into terephthalic acid (TPA) by acid. This process is already widely used in the recycling of polyethylene terephthalate fiber waste and reduction processing of PET cloth.

In some cases, it is claimed that a significant level of hydrolysis can be achieved with only the heat generated when alkali is dissolved in alcohol by adding an organic solvent for molecular chain swelling (eg DMSO) (Loop Industries USP9,550,713B1). However, even at this time, in the case of PET having a low degree of polymerization, such as fibers or packaging materials, it seems to be hydrolyzed for some time, even if not completely. It appears that there will be an insignificant level of hydrolysis.

The third method is the method of (c) of [Scheme 1], which uses EG as a solvent to glycolyze PET at high temperature and high pressure to decompose into bis(2-hydroxyethyl) terephthalate (BHET) and oligomers. This is the most widely used method for recycling PET (PET waste) from a long time ago by PET manufacturers. These reaction products can be mixed into the polymerization process and used for PET polymerization. In this case, it is mainly used as a reuse method of waste PET with less contamination generated during PET production. During PET polymerization, only high-purity raw materials are used because the degree of polymerization does not increase unless the high purity of the raw materials is maintained. because it is difficult to do

As such, these methods are all methods of reacting in an organic solvent and can be applied to PET with a low degree of polymerization and a relatively loose molecular chain state, but IV = 0.8 dl/ Such reactions are not easy when the degree of polymerization is high enough to exceed g and the molecular chains are densely packed. In fact, when the solid content of the mixed pulverized PET bottle (mixed pulverized water bottle, juice bottle, etc.) is about 30% by weight and subjected to alkaline hydrolysis in a high-pressure reaction tube under an alcohol solvent, the reaction pressure of 3 to 5 bar At the boiling temperature of alcohol and reflux, vigorously agitated and hydrolyzed for one week, more than 20% of non-hydrolyzed PET remains. In particular, in the case of heat-resistant PET bottles for juice beverages, they are produced through a two-stage blowing process that includes a heat-setting process that is much stronger than that of ordinary mineral water bottles, compared to general water bottles produced through a one-stage blowing process. It has a high molecular weight and a much higher crystallinity, and the molecular chain packing is also ultra-dense, so alkaline hydrolysis is much more difficult than general bottled water PET bottles. They do not dissolve easily in strong solvents such as hexafluoroisopropanol (HFIP) (1)-trifluoroacetic acid [(1)-Trifluoroacetic acid: TEA], which is a solvent used in PET IV measurement, and leave a significant amount of undissolved matter. As a result, more undecomposed residues are produced during normal hydrolysis. The surface of these residues is swollen in the solvent and clumps together like rice cakes, sticking to the walls of the reactor and the agitator, which makes the reactor inoperable and also blocks the discharge port of the reactor, making normal discharge impossible. Alcohols used as general hydrolysis solvents, such as methanol and ethanol _, showed similar hydrolysis results even though there was a difference in solvent polarity _. The results were not significantly improved.

Like fibers, PET with an IV of about 0.55 dl/g and a medium or low degree of polymerization is completely decomposed into monomers within 1 hour when heated under reflux by acid or alkali in a polar organic solvent. Even in this case, for rapid hydrolysis, a toxic and explosive organic solvent must be used as a reaction solvent, and a large amount of strong acid or alkali must be used.

In the case of high polymerization degree PET with an intrinsic viscosity of 0.75 dl/g or more, as mentioned above, some decomposition starts on the surface when hydrolyzed by a known method, but the degree of polymerization is high, so the decomposition does not proceed to the inside anymore and swelling occurs on the surface. ) only occurs. When the surface changes like a gel and becomes viscous, the PET pieces stick to each other even when vigorously stirred. As a result, it is impossible for acids and alkalis to permeate into the inside any more, so that the decomposition reaction rate drops drastically, so that smooth reactions are no longer possible. At least, the way to minimize this phenomenon is to grind the sample PET as finely as possible, but PET is highly amorphous, so it is not easy to physically grind it at room temperature. In particular, in the case of PET bottles, it is difficult to grind them into a powder state, so they are used by tearing them into pieces as small as possible. In general, plastics are pulverized using a liquid nitrogen cryogenic mill (Liquid N2 freezer ball mill) or a ball-mill. Crystalline polymers or polymers with high hardness are pulverized relatively well, but PET is difficult to pulverize because of its amorphous nature. It doesn't work out. Moreover, in the case of high-polymerization PET having an intrinsic viscosity of 0.75 dl/g or more, it is much more difficult, and in terms of economic efficiency, such a grinding method is completely meaningless.

For these reasons, until now, PET bottles with a high degree of polymerization have hardly been economically chemically recycled, and are mainly made into low-grade fibers such as cotton for filling or staple fibers through simple melt spinning after washing and drying. Recycling is mainly done.

There are the following important problems in the chemical decomposition of PET as mentioned above.

First, although there is a difference in degree, in the existing methods, there is a problem in that a toxic and highly flammable low boiling point organic solvent is used as a reaction solvent, and heating and pressurization reactions are required for rapid reaction. The most commonly used solvents for alkaline hydrolysis include alcohols such as ethanol, methanol, etc., which are toxic to the skin and eyes to varying degrees. The risk of explosion is great.

Second, in the case of EG depolymerization, substances such as cyclic oligomers and butylated hydroxytoluene (BHT), which are harmful to the human body, are generated, and repolymerization into PET for bottled water and food containers may pose a threat to health.

In the case of hydrolysis with the addition of organic solvents for swelling such as dimethyl sulfoxide (DMSO) and dichloromethane (CH ₂ Cl ₂ ), they must be separated again after the reaction, and it is difficult to obtain high-purity monomer products due to by-products. In order to obtain a high-purity product, significant additional refinery facilities are required. In addition, in many cases, the final decomposition product is dimethyl terephthalate (DMT) rather than terephthalic acid (TPA), and in that case, more various monomers and oligomers including terephthalic acid (TPA) are produced as impurities. It is almost impossible and it is more difficult to use it as a raw material for PET polymerization that requires ultra-high purity.

Thirdly, as a more critical problem, in the case of high polymerization degree PET having an intrinsic viscosity of 0.75 dl / g or more, there is a problem that decomposition such as (a), (b), (c) of [Scheme 1] is not easy. The most representative product of high-polymerization PET with an intrinsic viscosity of 0.75 dl/g or more is PET bottled water bottles, and PET heat-resistant bottles for juice are difficult to disassemble due to high crystallinity, and high-tenacity yarns such as PET tire cords that require stronger mechanical properties. IV=1.0~1.2㎗/g even goes up.

In the case of PET bottles, the degree of polymerization is high, but high elongation and heat setting in the manufacturing process result in a cross-packing state in which molecular chains are densely stacked. Due to this, it is difficult for the reaction solvent or alkali to permeate between molecules during the decomposition reaction, making it difficult for the reaction to proceed from the surface to the inside.

In the present invention, it is intended to provide a method for producing terephthalic acid in high yield and good process stability by hydrolyzing polyethylene terephthalate having a high polymerization degree having an intrinsic viscosity of 0.75 dl/g or more without using an organic solvent.

Specifically, the object of the present invention is to solve the problems related to the safety and low reactivity to organic solvents as described above in the economical hydrolysis reaction of PET, and in particular, a high polymerization degree having an intrinsic viscosity of 0.75 dl/g or more, such as a PET bottle, which is difficult to react. It is intended to solve problems such as the low reactivity of PET at the same time.

In order to achieve the above object, in the present invention, (i) after introducing high polymerization degree polyethylene terephthalate having an intrinsic viscosity of 0.75 dl / g or more into a continuous reactor, heating and pressurizing to prepare fluid polyethylene terephthalate, (ii) ) A mixed slurry prepared by mixing an alkali containing an alkali metal, a weak acid salt of the alkali metal, and ethylene glycol is introduced into the interior of the continuous reactor through which the fluid polyethylene terephthalate passes, thereby producing fluid polyethylene in the continuous reactor. Neat reaction of terephthalate and the mixed slurry to prepare alkali metal terephthalate, (iii) dissolving the prepared alkali metal terephthalate in water, removing foreign substances through filtration and centrifugation, and dissolving in water Terephthalic acid is produced by reacting alkali metal terephthalate with acid.

Specifically, unlike the conventional decomposition reaction in which an organic solvent such as ethanol or methanol is added as a reaction solvent to a batch reactor, an extruder-type continuous reactor is used to melt without a separate reaction solvent. The PET itself is a reactant and also acts as a solvent, and it undergoes a continuous decomposition reaction with a neat reaction. In a continuous reactor, the reaction temperature and pressure are adjusted to melt PET, and a mixture of catalyst-level ethylene glycol (EG), an alkali metal-based alkali, and a weak acid salt of the alkali metal is added thereto. For example, when NaOH is used as an alkali, Na ₂ CO ₃ , which is a salt of NaOH and a weak acid H ₂ CO ₃ , is added. As shown in [Scheme 2] below, when PET is hydrolyzed, disodium terephthalate (TPA-Na ₂ ) and ethylene glycol (EG) are formed, and the Na+ concentration gradually decreases, so that the hydrolysis reaction rate gradually decreases. do. However, at this time, if there is Na ₂ CO ₃ , a weak salt of Na+, it also dissolves in ethylene glycol (EG), a polar solvent, and more Na+ is created, which plays a role in further increasing the concentration of Na+ along with the concentration of Na+ generated from NaOH. more NaO-C ₂ H ₂ -ONa. This keeps the concentration of Na+ from decreasing due to the hydrolysis reaction of PET, and keeps the reaction rate fast.

[Scheme 2]

[Correction under Rule 91 18.05.2022]

Then, when the hydrolysis of PET starts, the EG generated at the beginning serves as a solvent and at the same time acts as an accelerating catalyst, so that the hydrolysis reaction proceeds more rapidly.

In order to maintain a fast reaction rate and increase the reaction rate, it is very important to properly control the reaction temperature and pressure. During the entire reaction period, it is preferable to keep the reaction temperature as low as possible. This is because the generation of impurities due to side reactions is reduced and the reaction pressure is lowered, making it easy to control the reaction. After initially melting PET, if an alkali and a weak acid salt of the alkali are mixed with the melted PET as shown in [Scheme 2] above, the hydrolysis reaction proceeds rapidly and the molecular weight rapidly decreases. As a result of the reaction, TPA-Na ₂ salt (Salt) and ethylene glycol (EG) are produced. The TPA-Na ₂ salt (Salt) produced at this time is a solid powder, and another product, ethylene glycol (EG), is a liquid. TPA-Na ₂ is The boiling temperature is 392.4 ° C. at 1 atm, so it is very stable in temperature, but ethylene glycol (EG) has a boiling temperature of 197 ° C. This is because EG generated during the hydrolysis reaction must be kept in a liquid state without vaporization so that it is uniformly mixed with the molten PET to act as a solvent and partially become Na-OC ₂ H ₄ O-Na to further promote the hydrolysis reaction. am.

20 is a graph showing the correlation between the temperature and vapor pressure of EG. In order for EG to maintain a liquid state at a specific temperature, a pressure higher than the corresponding vapor pressure must be applied. For example, the boiling temperature of EG at 1 atm is 197°C, and the vapor pressure is 760 mmHg. At 260° C., which is the melting temperature of PET, it has a vapor pressure of about 4000 mmHg (about 5.3 atm).

In the actual process, when PET decomposes and EG starts to form, the molecular weight of PET rapidly decreases, and PET maintains a molten state even when the reaction temperature is maintained at 20 to 30 ° C lower than 260 ° C. At this time, the EG vapor pressure is below 2000 mmHg. Even if a high pressure of 5.3 atmospheres or more is not applied and only a reaction pressure of about 2.5 to 3 atmospheres is maintained, EG can be maintained in a liquid state and a fast hydrolysis reaction rate can be maintained. In this way, in order to keep the reaction temperature low and improve the mixing effect, a method of dividing the alkali into two times is used. First, when PET is first supplied to the continuous reactor (extruder), a small amount of alkali (e.g., NaOH) is mixed with it, which causes the primary hydrolysis to decrease the average molecular weight of PET and lower the melting temperature. At the same time, it is mixed with a small amount of EG, resulting in a lower viscosity, which makes the reaction conditions milder and easier to control the decomposition reaction. Then, for a full-scale decomposition reaction, a mixed slurry of an alkali containing an alkali metal, a weak salt of the alkali metal, and ethylene glycol is mixed in a reaction zone 2, which is a mixing zone of a continuous reactor having a much lower reaction temperature, in a sufficient amount for the reaction Even if the input amount is large, the viscosity of PET is lowered due to the primary hydrolysis, making mixing much easier.

As such a continuous reactor, an extruder is used as the most common reactor because it is possible to combine the screws used in the extruder with other spiral types. In other words, it is possible to set the characteristics of the device according to the reaction conditions such as temperature and pressure, which are different for each reaction zone, and because it is continuous, high yield can be obtained even with a small device. Of course, when using a high-efficiency twin screw extruder, it is possible to react much faster and with higher yield than when using a single screw extruder due to higher mixing efficiency.

According to the present invention, terephthalic acid can be produced in high yield and good process safety from polyethylene terephthalate having a high degree of polymerization having an intrinsic viscosity of 0.75 dl/g or more, which is difficult to hydrolyze even with an organic solvent due to a high degree of polymerization, without using an organic solvent.

The present invention can rapidly hydrolyze high polymerization degree PET having an intrinsic viscosity of 0.75 dl/g or more, which has been difficult to hydrolyze in the past, through a Neat reaction without using a toxic organic solvent. In addition, since the reaction temperature is lower than the melting temperature of PET in a short time, it is possible to obtain only pure hydrolyzates with almost no side reactants due to thermal decomposition. Above all, the fact that low boiling point organic solvents, which are toxic and have a high fire risk, are not used significantly improves the safety of the process.

1 is a schematic diagram of a process for preparing an alkali metal terephthalate by adding high polymerization degree PET having an intrinsic viscosity of 0.75 dl/g or more and NaOH, EG, and Na ₂ CO ₃ to an extruder to perform a neat reaction.

Figure 2 is a cross-sectional view showing the form of a screw (Screw) constituting the extruder of Figure 1 by way of example.

3 is a Raman spectroscopy spectrum of high polymerization degree PET having an intrinsic viscosity of 0.75 dl/g or more used in Examples of the present invention.

Figure 4 is a Raman spectroscopy spectrum of sodium terephthalate as a standard.

5 is a Raman spectroscopy spectrum of terephthalic acid as a standard.

6 is a Raman spectroscopy spectrum of sodium terephthalate prepared in Example 1;

7 is a Raman spectroscopy spectrum of terephthalic acid prepared in Example 2;

8 is a Raman spectroscopy spectrum of sodium terephthalate prepared in Comparative Example 1;

9 is a Raman spectroscopy spectrum of sodium terephthalate prepared in Comparative Example 2;

10 is a Raman spectroscopy spectrum of sodium terephthalate prepared in Comparative Example 3;

11 is a Raman spectroscopy spectrum of sodium terephthalate prepared in Comparative Example 4;

12 is a Raman spectroscopy spectrum of terephthalic acid prepared in Comparative Example 5.

13 is a Raman spectroscopy spectrum of sodium terephthalate prepared in Comparative Example 6;

14 is a Raman spectroscopy spectrum of sodium terephthalate prepared in Comparative Example 7;

15 is a Raman spectroscopy spectrum of terephthalic acid prepared in Comparative Example 8;

16 is a Raman spectroscopy spectrum of the potassium terephthalate salt prepared in Example 3.

17 is a Raman spectroscopy spectrum of terephthalic acid prepared in Example 4.

18 is a SEM-EDS distribution photograph of Na at a magnification of 500 times obtained in Comparative Example 9.

19 is a SEM-EDS distribution photograph of Na at a magnification of 500 times obtained in Example 5.

20 is a graph showing the correlation between temperature and vapor pressure of EG.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The present invention (i) polyethylene terephthalate (PET) having a degree of polymerization of 0.75 dl / g or more is put into a continuous reactor in the form of an extruder and then heated and pressurized to produce fluid polyethylene terephthalate. process; (ii) A mixed slurry prepared by mixing an alkali containing an alkali metal, a weak acid salt of the alkali metal, and ethylene glycol is introduced into the interior of the continuous reactor through which the fluid polyethylene terephthalate passes, and in the continuous reactor A step of preparing alkali metal terephthalate by neat (Neat) reaction of fluid polyethylene terephthalate and the mixed slurry; and (iii) dissolving the alkali metal terephthalate in water, removing foreign matter through filtration and centrifugation, and reacting the alkali metal terephthalate dissolved in water with acid to produce terephthalic acid. to be

Specifically, in the present invention, polyethylene terephthalate (PET) having a degree of polymerization of 0.75 dl/g or more is first introduced into a continuous reactor in the form of an extruder, and then heated and pressurized to produce fluid polyethylene terephthalate. do.

Polyethylene terephthalate having a degree of polymerization of 0.75 dl/g or more may be a homopolymer or a copolymer.

In the present invention, when polyethylene terephthalate having a degree of polymerization of 0.75 dl/g or more is introduced into an extruder-type continuous reactor, it is more preferable to add an alkali containing an alkali metal together.

The alkali content including the alkali metal introduced into the continuous reactor together with polyethylene terephthalate having a polymerization degree of 0.75 dl/g or more is adjusted to be 5 to 10% in weight ratio with the polyethylene terephthalate.

Next, a mixed slurry prepared by mixing an alkali containing an alkali metal, a weak acid salt of the alkali metal, and ethylene glycol is introduced into the interior of the continuous reactor through which the fluid polyethylene terephthalate passes, and the inside of the continuous reactor Alkali metal terephthalate is prepared by neat reaction of fluid polyethylene terephthalate and the mixed slurry.

At this time, it is preferable to divide the mixed slurry into 1 to 5 steps and introduce them at different positions of the continuous reactor through which the fluid polyethylene terephthalate passes.

The alkali metal containing the alkali metal and the alkali metal forming the weak acid salt of the alkali metal is lithium (Li), sodium (Na) or potassium (K).

The weak acid salt of the alkali metal is a salt produced by the reaction of an alkali metal and carbonic acid (H ₂ CO ₃ ), a salt produced by a reaction of an alkali metal and phosphoric acid (H ₃ PO ₄ ), a salt produced by a reaction of an alkali metal and acetic acid Salt or alkali metal and formic acid reaction, such as fish salt.

Next, after dissolving the alkali metal terephthalate in water, foreign substances are removed through filtration and centrifugation, and acid is added to the alkali metal terephthalate dissolved in water to react to prepare terephthalic acid.

The biggest feature of the present invention is that an organic solvent that is highly flammable and harmful to the human body is not used as a reaction solvent in the decomposition reaction, and alkali with alkali metals such as molten PET and KOH and NaOH is catalytically neutral in the presence of corresponding alkali metal salts. (Neat) is that it reacts. The advantage of the neat reaction is that there are no harmful compounds that act only as solvents regardless of the reaction, so it is very good in terms of safety, reaction efficiency, and speed.

In terms of reactivity, since there is no concentration dilution by the reaction solvent, a direct reaction occurs between the reactants (i.e., the reaction concentration is 100%), so the reaction rate is faster than when a solvent is used and side reactions are less, so the generation of impurities is significantly reduced. In the case of such a neat reaction, since the melt viscosity of PET is extremely high compared to that of a general organic solvent reaction, it is too difficult to mix the reactants in a batch reactor.

A very useful way to solve this problem is to use a mixing device such as an extruder as a reactor. In addition, in the reaction using an extruder, it is also very important that the reaction rate can be increased by lowering the reaction temperature and melt viscosity.

Looking at the process of the Neat reaction,

First, as shown in FIG. 1, PET is pushed and fluidized into an extruder having several reaction zones. At this time, the entire screw of the extruder is not of the same screw structure, but has a shape suitable for characteristics required for each reaction zone, as shown in FIG. 2.

The biggest consideration in setting the temperature of each reaction zone is the thermal characteristics of PET, such as the glass transition point (Tg: around 70℃), melting point (Tm: usually around 250~260℃), and boiling point of EG (b.p.: 197 ℃ 1 atm), etc., but when pressure is applied, these temperatures are naturally different from normal pressure.

A more detailed look at each reaction zone is as follows.

The first reaction zone 1 is a zone for PET supply and fluidization, and the PET solid pieces injected are pushed forward as they become fluid objects by the heat and pressure of the screw and block. At this time, when only PET is added, the melting temperature must be raised to fluidize the PET, but in this case, the melt viscosity is too high. For smooth supply and fluidization, when PET is mixed with 5 to 10% alkali by weight and the first hydrolysis reaction is performed simultaneously with PET supply, the melting point and viscosity are lowered, making it easier to supply.

In addition, the shape of the extruder screw is also important. In general, a screw with a larger pitch is used as the particle diameter of the input raw material is larger. . At this time, the starting temperature of the reaction zone 1, which is the PET supply zone, is maintained between the glass transition point (Tg) and the melting point (Tm) of PET, and is usually about 100 to 180 ° C so that the PET is first decomposed and melted. This is because it is well mixed with the secondary input alkali in the reaction zone 2, which is the second mixing zone.

The second reaction zone 2 is a mixing zone. Here, the screw is designed to mix the fluidized PET pushed from the reaction zone 1 with the alkali and increase the mixing efficiency. First, a mixing slurry prepared by mixing a small amount of EG with a slightly excess alkali (eg, NaOH, KOH) and a weak acid salt of an alkali metal (eg, Na ₂ CO ₃ , K ₂ CO ₃ ) is prepared. Then, as shown in [Scheme 3] below, EG and alkali MOH (M: alkali metal) react to form metal glycolates. In addition, a part of M ₂ CO ₃ , which is a metal salt, is dissociated to form M ⁺ and CO ₃ ^-2 ions, which are all mixed. At this time, the amount of M ⁺ ions should be 10 to 20% more than the equivalent ratio.

[Scheme 3]

Quantitatively push the mixing slurry into the mixing zone of the main extruder using a gear pump or a second feeding extruder and mix it well with fluid PET . In the reaction zone 2, the temperature is started lower than the PET Tm and gradually lowered to about 200 ° C near the end of the reaction zone 2. When fluidized PET passes through the end of reaction zone 1 and flows into reaction zone 2, the Tm of PET is lowered by primary decomposition. Due to the decrease in molecular weight due to this temperature factor and primary hydrolysis, the viscosity is lowered, so that the temperature of reaction zone 2 is properly adjusted to maintain the shear for mixing so that PET and the mixing slurry are well mixed. do. In reaction zone 2, some reactions proceed further as the two reactants are mixed, but the reaction is completed in the third reaction zone 3 and the fourth reaction zone 4, and a screw structure is adopted to improve mixing efficiency.

At the end of the reaction zone 2, the temperature of the reactants is about 150 to 200 ° C, and the temperature is adjusted so that it can pass to the next reaction zone 3.

Reaction zone 3 is the zone where the first reaction proceeds, and PET and metal glycolate react as shown in [Scheme 4], and most of the alkaline hydrolysis reaction of PET proceeds.

[Scheme 4]

[Correction under Rule 91 18.05.2022]

At this time, in order to steadily push the reactants forward while maintaining the reaction pressure, the pitch interval is narrower than the screw pitch interval of the reaction zone 1.

Such a decomposition reaction of PET is not disturbed even when other types of plastics such as polypropylene or polyethylene are mixed, and heterogeneous plastic mixtures remain unreacted and can be physically removed.

When NaOH, the most commonly used alkali, is used, the product is sodium terephthalate (Disodium terephthalate) and EG, but it is not completely hydrolyzed and becomes a mixture of oligomeric PET.

The reaction starting temperature of reaction zone 3 starts at about 150 ~ 200 ℃ from reaction zone 2, and the temperature is raised by about 20 ~ 30 ℃ to maximize the hydrolysis reaction rate. The temperature is maintained at 180 ~ 230 ℃ to maintain the melt viscosity that has fallen due to the decrease in molecular weight of PET according to the reaction, and the vapor pressure of the produced EG is kept as low as possible.

Reaction zone 4 is a zone where the secondary reaction proceeds, and the temperature starts at 180 ~ 230 ℃ and lowers the temperature to 180 ~ 200 ℃ while increasing the reaction rate to the maximum with a long residence time. At the end of the reaction zone 4, as a result of the reaction, PET is almost converted to a monomer, and the viscosity is very low with a small amount of the remaining oligomer. The temperature is controlled so that the viscosity and pressure are maintained.

The fifth reaction zone 5 is a zone where discharge proceeds and lowers the temperature to about 150 to 180 ° C. Solid products include alkali metal salts of the main component, terephthalic acid (hereinafter referred to as "TPA"), PET and oligomers that are not completely decomposed, and liquid products include EG and alkali metal glycolates. These products are discharged in a mixed slurry state. At this time, by appropriately adjusting the discharge temperature, the vapor pressure of EG, which is a liquid generating material, is lowered so that bumping due to the EG vapor pressure does not occur and the discharge is stably performed. The expelled material is cooled, solidified, and then pulverized into powder.

Each process product of this reaction was identified by Raman spectroscopy. Raman spectroscopy can measure the molecular structure of a solid-state sample as it is without pretreatment, so that the degree of reaction of each product of the present invention can be directly confirmed. In addition, the molecular weight change of PET was measured by IV, and the degree of Na distribution was confirmed using SEM-EDX to confirm the mixing performance of the extruder.

The reaction process goes through the process of PET → TPA-Na → TPA, and the characteristics of the largest molecular structural change are as follows.

In PET, a benzene ring and an ester carbonyl C=O are the most representative structures, and as shown in FIG. 3, a benzene ring peak at 1601 cm ^-1 and a large ester peak at 1714 cm ^-1 appear. This peak decreases in size as the ester bond of PET is converted to TPA-Na, and it can be used to determine how much PET is decomposed.

Sodium terephthalate (TPA-Na) is converted into sodium carboxylate CO-Na by decomposition of the ester structure. As shown in FIG. 4, the benzene ring peak is at the same position, but the ester peak at 1714 cm ^-1 gradually disappears and the peak of sodium carboxylate at the position of 1123 cm ^-1 gradually increases.

TPA is obtained by adding acid to sodium terephthalate (TPA-Na), Na is dropped and H is attached, and the terminal group is carboxylic acid -COOH. As a result, the peak of sodium carboxylate at 1123 cm ^-1 disappears as shown in FIG. A new carboxylic acid peak is generated at 823 cm ^-1 , and the benzene ring peak is also slightly shifted to emerge from the 1617 cm ^-1 position.

Based on this basic Raman spectrum, the compounds obtained in the experimental process are compared and confirmed.

The present invention will be examined in more detail through the following examples. However, the present invention is not limited to the following examples.

Example 1

Preparation of sodium salt of terephthalate

Using a twin extruder with 5 reaction zones (temperature control zone), the PET bottle pieces with IV=0.83dl/g and 5% NaOH by weight are well mixed and introduced, and then the second extruder After preparing a mixed slurry in which 30% of NaOH and 5% of Na ₂ CO ₃ are mixed with 15% of EG, it is introduced into the extruder reaction zone 2 to prepare sodium terephthalate.

The twin extruder can control the temperature with an electric heater and water cooling, and it is also possible to remove the gas generated by vacuum. The length:diameter ratio of the screw is 40:1.

At this time, the reaction zone 1, reaction zone 2, reaction zone 3, reaction zone 4 and reaction zone 5 temperatures were set to 160 ° C, 180 ° C, 220 ° C, 200 ° C and 170 ° C, respectively.

The screw rotation speed is adjusted so that the residence time of PET in the extruder is about 10 minutes.

Cool the sodium terephthalate after the reaction is complete.

Figure 6 is a Raman spectroscopy spectrum taken of sodium terephthalate after the reaction. A very large peak comes out at the 1123 cm ^-1 position and the PET ester peak at the 1714 cm ^-1 position is greatly reduced to a level that is seen as a trace.

Example 2

terephthalic acid manufacturing

Dissolve 100 g of the sodium terephthalate salt obtained in Example 1 in 1 L of pure water while stirring. After about 10 minutes, the aqueous solution is filtered through a filter paper. Put the solids filtered out on the filter paper back into 1L of pure water and dissolve them well while stirring again. After 10 minutes, it was filtered again with a filter paper, and the filtered undissolved solid was 2 g as a result of weighing after drying, which means that the conversion reaction rate of PET → TPA-Na ₂ was about 98%. 1 L of the second filtrate is combined with 1 L of the first filtrate. Mix a small amount of hydrochloric acid with 2L of this filtrate, stir well, and measure the acidity (pH). Add hydrochloric acid until the acidity of the solution becomes slightly acidic (pH=4,5). Then, white precipitates fall, which are collected through filter paper, washed twice more with pure water, and then dried to produce terephthalic acid.

The results of measuring the Raman spectroscopy spectrum of the prepared terephthalic acid were shown in FIG. 7 .

Example 3

Manufacture of potassium terephthalate salt

Mix the PET bottle pieces with IV=0.83dl/g and 5% KOH by weight well in the twin extruder, and then add 35% KOH and 5% KOH using the second extruder. Potassium terephthalate salt was prepared under the same conditions as in Example 1, except that a mixed slurry in which K ₂ CO ₃ was mixed with 15% EG was secondarily added.

The Raman spectroscopy spectrum of the prepared potassium terephthalate salt was the same as in FIG. 16, and FIG. 16 was almost similar to the Raman spectroscopy spectrum of the sodium terephthalate salt, but it could be seen that there were some differences in the peak intensity ratio.

Example 4

terephthalic acid manufacturing

Dissolve 100 g of the potassium terephthalate salt obtained in Example 3 in 1 L of pure water while stirring. After about 10 minutes, the aqueous solution is filtered through a filter paper. Put the solids filtered out on the filter paper back into 1L of pure water and dissolve them well while stirring again. After 10 minutes, it was again filtered with a filter paper, and the filtered undissolved solid was about 4 g as a result of weighing after drying, which means that the conversion reaction rate of PET → TPA-K2 was about 96%. 1 L of the second filtrate is combined with 1 L of the first filtrate. Mix a small amount of hydrochloric acid with 2L of this filtrate, stir well, and measure the acidity (pH). Add hydrochloric acid until the acidity of the solution becomes slightly acidic (pH=4,5). Then, white precipitates fall, which are collected by filtering, washed twice more with pure water, and then dried to produce terephthalic acid. The results of measuring the prepared terephthalic acid Raman spectrometer spectrum are shown in FIG. 17, and it can be seen that the dried white solid precipitate material is TPA from the result of comparison with the Raman spectrometer spectrum of the standard TPA in FIG. 5.

Example 5

Alkali powder mixing test using NaCl 2

Under the same test conditions as in Example 1, 10% NaCl powder by weight was mixed with PET and added. As a result of measuring SEM-EDS at 500 times after the discharge was cooled to room temperature and hardened, as shown in FIG. 19, Na (light blue) and C (red) elements derived from PET were finely mixed without large lumps. This means that the powders of NaCl are evenly distributed. This shows that when the total amount of NaOH is added to PET, firstly mixing a small amount and secondly adding it gradually causes the viscosity of PET to decrease gradually through a gradual decomposition reaction, and the mixing becomes much more uniform. This explains why the reaction is much more uniform and goes well when NaOH is added in parts rather than at once.

Comparative Example 1

Preparation of sodium salt of terephthalate

Using a twin extruder with 5 reaction zones (temperature control zone), IV=0.83dl/g PET bottle pieces and NaOH are reacted to prepare sodium terephthalate (TPA-Na ₂ ) . The twin extruder can control the temperature with an electric heater and water cooling, and it is also possible to remove the gas generated by vacuum. The length:diameter ratio of the screw is 40:1.

The PET pieces were uniformly mixed with NaOH at a weight ratio of 5% and then put into the extruder. At this time, the reaction zone 1, reaction zone 2, reaction zone 3, reaction zone 4 and reaction zone 5 temperatures were set to 160 ° C, 180 ° C, 220 ° C, 200 ° C and 170 ° C, respectively.

Cool the sodium terephthalate after the reaction is complete. IV of the prepared sodium terephthalate was measured to be 0.51 dl/g, and the Raman spectrometer spectrum was as shown in FIG. 8 . The drop in IV from 0.83 to 0.51 dl/g means that there was a certain level of decomposition reaction.

In addition, in the Raman spectrometer spectrum of FIG. 8, a small peak was generated at the position of 1123 cm ^-1 , indicating that PET was partially decomposed to produce sodium terephthalate (TPA-Na ₂ ).

Comparative Example 2

Preparation of sodium salt of terephthalate

Sodium terephthalate was prepared under the same conditions as in Comparative Example 1, except that PET bottle pieces having IV = 0.83 dl/g and 15% NaOH by weight were added to the twin extruder. The Raman spectroscopy spectrum of the reacted sodium terephthalate was shown in FIG. 9, and in FIG. 9, a very large peak appeared at the 1123 cm ^-1 position and the PET ester peak at the 1714 cm ^-1 position was reduced by almost half, smaller than 1123 cm ^-1 As for the intensities of the two peaks, it can be seen that the 1123 cm ^-1 peak, which indicates the amount of sodium terephthalate (TPA-Na ₂ ), is about 1.2 times larger.

Comparative Example 3

Preparation of sodium salt of terephthalate

Sodium terephthalate was prepared under the same conditions as in Comparative Example 1, except that PET bottle pieces having IV = 0.83 dl/g and 30% NaOH by weight were added to the twin extruder. The Raman spectroscopy spectrum of the reacted sodium terephthalate is shown in FIG. 10, and in FIG. 10, a very large peak comes out at the 1123 cm ^-1 position and the PET ester peak at the 1714 cm ^-1 position is greatly reduced so that the intensity is 1123 cm ^- It can be seen that it is reduced to about 1/16 level compared to ^{the 1} peak.

Comparative Example 4

Preparation of sodium salt of terephthalate

Mix the PET bottle pieces with IV = 0.83dl/g and 5% NaOH by weight into the twin extruder first, and then use the second extruder to mix 30% NaOH with 15% NaOH. Sodium terephthalate was prepared under the same conditions as in Comparative Example 1, except that the mixed slurry mixed with EG was secondarily added. The Raman spectroscopy spectrum of sodium terephthalate after the reaction was completed was shown in FIG. 11, and in FIG. 11, a very large peak appeared at the 1123 cm ^-1 position and the PET ester peak at the 1714 cm ^-1 position was greatly reduced, resulting in an intensity of 1123 cm ^- Although it is reduced to about 1/18 level compared to ^{the 1} peak, it can be seen that there is still undecomposed PET.

Comparative Example 5

terephthalic acid manufacturing

Dissolve 100 g of sodium terephthalate obtained in Comparative Example 4 in 1 L of pure water while stirring. After about 10 minutes, the aqueous solution is filtered through a filter paper. Put the solids filtered out on the filter paper back into 1L of pure water and dissolve them well while stirring again. After 10 minutes, it was filtered again with filter paper, and the filtered undissolved solid was 13 g as a result of weighing after drying, which means that the conversion reaction rate of PET → TPA-Na was about 87%. 1 L of the second filtrate is combined with 1 L of the first filtrate. Mix a small amount of hydrochloric acid with 2L of this filtrate, stir well, and measure the acidity (pH). Add hydrochloric acid until the acidity of the solution becomes slightly acidic (pH=4,5). Then, white precipitates fall, which are collected by filtering, washed twice more with pure water, and then dried to produce terephthalic acid. The results of measuring the Raman spectroscopy spectrum of the prepared terephthalic acid were shown in FIG. 12. From the results of comparison with the Raman spectroscopy spectrum of the standard TPA in FIG. 5 , it can be seen that the prepared white solid material is TPA.

Comparative Example 6

Preparation of sodium terephthalate salt using ethanol as a solvent

Install a stirrer, thermometer, and reflux condenser in a 1 liter four-necked round bottom flask and mount it on a heating mantle. Here, 100 grams of PET bottle pieces with IV = 0.83 dl/g, 30 milliliters of ethylene glycol sodium salt, 40 grams of sodium hydroxide, and 600 ml of ethanol are put. Increase the temperature of the heating mantle until ethanol boils, turn the stirrer to reflux, and react for about 10 hours. After the reaction, the reaction solution was filtered through a 100 mesh sieve to filter out unreacted residual PET bottle pieces, and then wiped with 100 ml of pure ethanol. As a result of weighing the filtered unreacted materials after drying, the weight was 23 g. This shows that the high polymerization degree PET having an intrinsic viscosity of 0.75 dl/g or more has a decomposition reaction rate of about 77%.

The emulsion reaction solution having a white precipitate from which unreacted PET pieces are removed is filtered using a paper filter to obtain a white precipitate. The obtained white precipitate was washed with methanol three times and dried to prepare sodium terephthalate.

The obtained sodium terephthalate was well soluble in water, and the spectrum was measured with a Raman spectrometer as shown in FIG. 13. As a result of comparing this with the Raman spectrometer spectrum of sodium terephthalate, which is the standard of FIG. 4, it was confirmed that the component was sodium terephthalate.

Comparative Example 7

Preparation of sodium terephthalate salt using ethanol as a solvent

Install a stirrer, thermometer, and reflux condenser in a 1 liter four-necked round bottom flask and mount it on a heating mantle. Here, 100 grams of finely cut bright PET cloth pieces with IV = 0.55 dl/g, 30 milliliters of ethylene glycol sodium salt, 40 grams of sodium hydroxide, and 600 ml of ethanol are added. Raise the temperature of the heating mantle until the ethanol boils, turn the stirrer to reflux, and react for about 1 hour. After the reaction, the reaction solution was filtered through a 100 mesh sieve to filter out unreacted PET bottle pieces, and then wiped with 100 ml of pure ethanol. There were no filtered unreactants. This means that the decomposition reaction rate of medium and low polymerization degree PET is good at almost 100%.

The emulsion filtrate having a white precipitate from which unreacted substances have been removed is filtered using a paper filter to obtain a white precipitate. The obtained white precipitate was washed with methanol three times and dried to prepare sodium terephthalate.

The obtained sodium terephthalate was well soluble in water, and the result of measuring the spectrum with a Raman spectrometer was as shown in FIG.

Comparative Example 8

Preparation of terephthalic acid

100 g of sodium terephthalate obtained in Comparative Example 7 was placed in a 2 liter beaker, and 1.5 liters of distilled water was added thereto and stirred to dissolve completely. Then, while adding hydrochloric acid little by little, stir well to make the solution slightly acidic (about pH = 4,5). A white precipitate then falls out. After filtering it with filter paper, it is dried to produce terephthalic acid.

The Raman spectrometer spectrum of the prepared terephthalic acid was as shown in FIG. 15, and as a result of comparison with the standard Raman spectrometer spectrum of FIG. 5, it could be confirmed that the terephthalic acid was terephthalic acid.

Comparative Example 9

Alkali powder mixing test using NaCl

Under the same reaction conditions as in Comparative Example 3, about 10% of NaCl powder by weight was mixed with PET and added. As a result of measuring SEM-EDS at 500 times after the excipient was cooled to room temperature and hardened, as shown in FIG. A picture was obtained, which shows that the decomposition reaction occurs too rapidly due to the input of a large amount of NaOH at once, so that the difference in PET viscosity by location is large and the change is non-uniform. This shows that when NaOH is added at once under the operating conditions of the twin extruder used in the experiment, it is not mixed well during the mixing process.

Claims

(i) a process of producing fluid polyethylene terephthalate by heating and pressurizing polyethylene terephthalate (PET) having a degree of polymerization of 0.75 dl/g or more into an extruder type continuous reactor;

(ii) A mixed slurry prepared by mixing an alkali containing an alkali metal, a weak acid salt of the alkali metal, and ethylene glycol is introduced into the interior of the continuous reactor through which the fluid polyethylene terephthalate passes, and in the continuous reactor A step of preparing alkali metal terephthalate by neat (Neat) reaction of fluid polyethylene terephthalate and the mixed slurry; and

(iii) dissolving the alkali metal terephthalate in water, removing foreign substances through filtration and centrifugation, and adding acid to the alkali metal terephthalate dissolved in water to react to produce terephthalic acid; characterized by comprising a Method for producing terephthalic acid using high polymerization polyethylene terephthalate having an intrinsic viscosity of 0.75 dl / g or more.
The high polymerization degree polyethylene having an intrinsic viscosity of 0.75 dl/g or more according to claim 1, wherein the mixed slurry is divided into steps 1 to 5 at different positions of the continuous reactor through which the fluid polyethylene terephthalate passes. Method for producing terephthalic acid using terephthalate.
The method of claim 1, wherein the polyethylene terephthalate having a degree of polymerization of 0.75 dl/g or more is one selected from a homopolymer and a copolymer, and has a high degree of polymerization having an intrinsic viscosity of 0.75 dl/g or more. Method for producing terephthalic acid using polyethylene terephthalate.
The method of claim 1, wherein the polyethylene terephthalate having a polymerization degree of 0.75 dl / g or more has an intrinsic viscosity characterized in that an alkali containing an alkali metal is added together when the polyethylene terephthalate is introduced into an extruder type continuous reactor. A method for producing terephthalic acid using polyethylene terephthalate having a high polymerization degree of 0.75 dl/g or more.
The method of claim 4, characterized in that the alkali content including the alkali metal introduced into the continuous reactor together with polyethylene terephthalate having a polymerization degree of 0.75 dl/g or more is adjusted to 5 to 10% in weight ratio with the polyethylene terephthalate. Method for producing terephthalic acid using high polymerization degree polyethylene terephthalate having an intrinsic viscosity of 0.75 dl / g or more.
The method of claim 1, wherein the alkali metal containing the alkali metal and the alkali metal constituting the weak acid salt of the alkali metal is one selected from lithium (Li), sodium (Na) and potassium (K), characterized in that the intrinsic viscosity is 0.75 Method for producing terephthalic acid using polyethylene terephthalate having a high polymerization degree of ㎗ / g or more.
The method of claim 1, wherein the weak acid salt of the alkali metal is a salt produced by the reaction of an alkali metal and carbonic acid (H 2 CO 3 ), a salt produced by the reaction of an alkali metal and phosphoric acid (H 3 PO 4 ), an alkali metal and Method for producing terephthalic acid using high polymerization degree polyethylene terephthalate having an intrinsic viscosity of 0.75 dl / g or more, characterized in that it is one selected from salts produced by the reaction of acetic acid and salts produced by the reaction of alkali metals and formic acid.